The present invention relates to a gas generating agent for air bags, and particularly, to a novel gas generating agent having excellent capabilities of collecting slag and generating reduced harmful gas.
An airbag system, which is a rider protecting system, has been widely adopted in recent years for improving safety of the riders in an automobile. The airbag system operates on the principle that a gas generator is operated under control of signals from a sensor detecting a collision, to inflate an airbag between riders and an car body. The gas generator is required to have a function to produce a required and sufficient amount of clean gas containing no harmful gas in a short time.
On the other hand, the gas generating agents are press-formed into a pellet form for stability to the burning, and the pellets and equivalent are required to maintain their initial flammability characteristics over a long time even under various harsh environments. In the event that the pellets deform or decrease in strength due to deterioration with age, change of environments and the like, the flammability of the explosive compositions will exhibit at an abnormally earlier time than the initial flammability, so there is a fear that the airbag or the gas generator itself may be broken with the abnormal combustion in case of a collision, to fail in accomplishing the aim of protecting the riders or oven cause them injury. To satisfy those required functions, gas generating agents containing metallic compound azide, such as sodium azide and potassium azide, as their major component have been used hitherto. These known gas generating agents are widely used in terms of their advantages that they are burnt momentarily; that the component of combustion gas is substantially nitrogen gas only, so that no harmful gas such as CO (carbon monoxide) or NOx (nitrogen oxide) is produced; and that since the burning velocity is little influenced by the environment or the structure of the gas generator, it is easy to design the gas generator. However, the azide produced by contact of the metallic compound azide and the heavy metal has the nature of being easily exploded by impact and friction, so that it must be handled with the greatest possible caution. Further, the metallic compound azide itself is a harmful material and further has a notable disadvantage that it can decompose in the presence of water and acid to produce harmful gas.
Accordingly, as the substitution of metallic compound azide, gas generating agents containing tetrazoles, azodicarbonamides and other nitrogenous organic compounds as fuel components have been proposed by, for example, Japanese Laid-open Patent Publications No. Hei 2(1990)-225159, No. Hei 2(1990)-225389, No. Hei 3(1991)-20888, No. Hei 5(1993)-213687, No. Hei 6(1994)-80492, No. Hei 6(1994)-239684 and No. Hei 6(1994)-298587. The tetrazoles in particular have a high proportion of atoms of nitrogen in their molecular structure and inherently have the function to suppress the production of CO such that production of CO can be suppressed, so that almost no CO is produced in the combustion gas, as in the case of the metallic compound azide. Besides, the tetrazoles are superior to the abovesaid metallic compound azide in far less danger and toxicity.
Chlorates, such as alkaline metals or alkaline earth metals, perchlorates or nitrates are generally used for oxidizing agents using the nitrogenous organic compounds as fuel to be burnt. The alkaline metals or the alkaline earth metals produce oxides as a result of the burning reaction, and the oxides are harmful materials for a human body and environment such that they must be in the form of easily collectable slag to be collected in the gas generator so that they can be prevented from being released into the air bag. However, since many of the gas generating agents using the nitrogenous organic compounds as fuel to be burnt have the heat of combustion as high as 2,000-2,500 joule/g or more, the gas generated becomes high in temperature and pressure. As a result of this, the slag which is a by-product obtained in the burning of the gas generating agents increase in temperature and thus increase in flowability. In a conventional type of gas generator, a filter fitted therein tends to reduce its slag collection efficiency. For increase of the slag collection efficiency, a method of increased number of filtering members being set in the filter to cool and solidify the slag may be practical, but such a method has a disadvantage of increasing the size of the gas generator, going against the trend toward the size reduction and weight reduction of the gas generator.
Also, various methods of addition of slag forming agents have been proposed for collecting the oxide of alkaline metal or alkaline earth metal in the form of the slag to be easily collected in the filtering part with efficiency. In these methods, silicon dioxide or aluminum oxide is in principle added as an acid substance or a neutral substance easily slag-reactable with the oxides which are basic substances. The proposed methods are conceptually the same as the conventional slag-forming method for the gas generating agent using metallic compound azide as the fuel. The proposed method is the method in which silicate or aluminate is used as the oxide and is converted into a high-viscosity or high-melting, glassy substance, to collect the oxide as the slag. Japanese Laid-open Patent Publication No. Hei 4(1992)-265292, in particular, discloses the method in which a low-temperature slag-forming substance as typified by silicon dioxide and a high-temperature slag-forming forming agent (e.g. alkaline earth metal or transition-metallic oxide) which produces a solid having a melting point close to or more than the reaction temperature are both added to allow high-melting particles, which are solid matters produced by burning reaction, to react with low-temperature slag-forming agents in molten condition and the resultant particles are fused among themselves to improve the collecting efficiency.
However, the addition of the large amounts of substances that do not contribute to the generation of gas causes reduction of a relative proportion of the fuel components of the gas generating components, so that a rate of gasification is high, as compared with the known metallic compound azide, so that the advantage of the nitrogenous organic compound base fuels of holding promise of reducing the size of the gas generator may be impaired.
It is the primary object of the invention to solve the slag collecting problem which stands in the way of commercially practicing the nitrogenous organic compound base fuels. It is the secondary object of the invention to promote the size reduction of the gas generator through the full use of high rate of gasification of the nitrogenous organic compound base fuels. Further, it is the tertiary object of the invention to provide a gas generating agent molded member which is strong and stable with age by improving heat resistant properties and formability of the nitrogenous organic compound base fuels which are poor compared with the metallic compound azide of an inorganic matter.
The present invention provides means to solve these problems. A basic construction of the present invention comprises a fuel component of nitrogenous organic compound and an oxidizing agent as its major components, to which at least one metal nitride or metal carbide is added as a slag forming agent. The metal nitride and the metal carbide are allowed to react with a metallic component or an oxide thereof contained in the fuel component or the oxidizing agent, to form slag.
Another basic construction of the gas generating agent comprises a fuel component of nitrogenous organic compound and an oxidizing agent as its major components, to which at least one metal nitride or metal carbide and a slag forming metallic component that is allowed to react with a metallic component of the metal nitride or the metal carbide or an oxide thereof, to form high-viscosity slag are added in the form of an element (a simple substance) or a compound.
Preferable as the metal nitride used in the present invention is at least one metal nitride selected from the group consisting of silicon nitride, boron nitride, aluminum nitride, magnesium nitride, molybdenum nitride, tungsten nitride, calcium nitride, barium nitride, strontium nitride, zinc nitride, sodium nitride, copper nitride, titanium nitride, manganese nitride, vanadium nitride, nickel nitride, cobalt nitride, iron nitride, zirconium nitride, chromium nitride, tantalum nitride, niobium nitride, cerium nitride, scandium nitride, yttrium nitride and germanium nitride.
Also, preferable as the metal carbide is at least one metal carbide selected from the group consisting of silicon carbide, boron carbide, aluminum carbide, magnesium carbide, molybdenum carbide, tungsten carbide, calcium carbide, barium carbide, strontium carbide, zinc carbide, sodium carbide, copper carbide, titanium carbide, manganese carbide, vanadium carbide, nickel carbide, cobalt carbide, iron carbide, zirconium carbide, chromium carbide, tantalum carbide, niobium carbide, cerium carbide, scandium carbide, yttrium carbide and germanium carbide.
Further, the metal nitride or the metal carbide may be pulverized into impalpable powder, adding thereto the fuel component and the oxidizing agent when pulverized, so that they can be allowed to have the function as a consolidation preventing agent therefor. A common consolidation preventing agent may be included as a consolidation preventing agent.
The slag forming metallic component that can be allowed to react with the metal nitride or the metal carbide in a combustion process to form the high-viscosity slag may be contained in the fuel component or the oxidizing agent or may alternatively be added in the form of an element (a simple substance) or another compound.
The slag forming metallic component includes at least one selected from the group consisting of silicon, boron, aluminum, alkaline metals, alkaline earth metals, transition metals and rare earth metals.
It is also a preferable form that the slag forming metallic component is added in the form of hydrotalcites for which the general chemical formula is as follows:
(M2+1xe2x88x92xM3+x(OH)2x+(Anxe2x88x92x/n.mH2O)xxe2x88x92
where
M2+ represents bivalent metal including Mg2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+ and Zn2+;
M3+ represents trivalent metal including Al3+, Fe3+, Cr3+, Co3+ and In3+;
Anxe2x88x92 represents an n-valence anion including OHxe2x88x92, Fxe2x88x92, Clxe2x88x92, NO3xe2x88x92, CO32xe2x88x92, SO42xe2x88x92, Fe(CN)63xe2x88x92, CH3COOxe2x88x92, oxalate ion and salicylate ion; and
0 less than xxe2x89xa60.33.
Preferable as the hydrotalcites is synthetic hydrotalcite for which the chemical formula is Mg6Al2(OH)16CO3.4H2O or pyroaurite for which the chemical formula is Mg6Fe2(OH)16CO3.4H2O.
The nitrogenous organic compound includes at least one nitrogenous organic compound selected from the group consisting of tetrazole, aminotetrazole, bitetrazole, azobitetrazole, nitrotetrazole, nitroaminotetrazole, triazole, nitroguanidine, aminoguanidine, triaminoguanidine nitrate, dicyanamido, dicyandiamido, carbohydrazide, hydrazocarbonamido, azodicarbonamide, oxamide and ammonium oxalate or their salts of alkaline metals, alkaline earth metals or transition metals. Of these nitrogenous organic compounds, tetrazole, aminotetrazole, bitetrazole, azobitetrazole, nitrotetrazole, nitroaminotetrazole, triazole are of preferable.
The oxidizing agent includes at least one oxidizing agent selected from the group consisting of nitrates of alkaline metal or alkaline earth metal, chlorates of alkaline metal or alkaline earth metal, perchlorates of alkaline metal or alkaline earth metal and ammonium nitrates.
It is also preferable that at least one water-soluble polymer compound selected from the group consisting of polyvinyl alcohol, polypropylene glycol, polyvinyl ether, polymaleic copolymers, polyethylene imide, polyvinyl pyrrolidone, polyacrylamide, sodium polyacrylate and ammonium polyacrylate is added to the gas generating agent composition as a formability modifying agent.
It is also preferable that at least one lubricant selected from the group consisting of stearic acid, zinc stearate, magnesium stearate, calcium stearate, aluminum stearate, molybdenum disulfide and graphite is added to the gas generating agent composition.
The following can be cited as preferable examples of the gas generating agent composition.
{circle around (1)} A gas generating agent composition comprising 20 to 50 weight % 5-aminotetrazole; 30 to 70 weight % strontium nitrate; and 0.5 to 20 weight % silicon nitride.
{circle around (2)} A gas generating agent composition comprising 20 to 50 weight % 5-aminotetrazole; 30 to 70 weight % strontium nitrate; 0.5 to 20 weight % silicon nitride; and 2 to 10 weight % synthetic hydrotalcite.
{circle around (3)} A gas generating agent composition comprising 20 to 50 weight % 5-aminotetrazole; 30 to 70 weight % strontium nitrate; and 0.5 to 20 weight % silicon carbide.
{circle around (4)} A gas generating agent composition comprising 20 to 50 weight % 5-aminotetrazole; 30 to 70 weight % strontium nitrate; 0.5 to 20 weight % silicon carbide; and 2 to 10 weight % synthetic hydrotalcite.
{circle around (5)} A gas generating agent composition comprising 20 to 50 weight % 5-aminotetrazole; 30 to 70 weight % strontium nitrate; and 0.5 to 20 weight % silicon nitride, wherein a slag forming metallic compound comprising at least one slag forming metal selected from the group consisting of aluminum, magnesium, yttrium, calcium, cerium and scandium is further mixed in the range of 1:9 to 9:1 in a ratio of the silicon nitride to the slag forming metallic compound.
{circle around (6)} A gas generating agent composition comprising 20 to 50 weight % 5-aminotetrazole; 30 to 70 weight % strontium nitrate; and 0.5 to 20 weight % silicon carbide, wherein a slag forming metallic compound comprising at least one slag forming metal selected from the group consisting of aluminum, magnesium, yttrium, calcium, cerium and scandium is further mixed in the range of 1:9 to 9:1 in a ratio of the silicon carbide to the slag forming metallic compound.
{circle around (7)} The gas generating agent composition {circle around (5)}, {circle around (6)} wherein the slag forming metallic compound is at least one of oxide, hydroxide, nitride, carbide, carbonate and oxalate of the slag forming metal.
{circle around (8)} The gas generating agent composition {circle around (5)}, {circle around (6)} wherein the slag forming metallic compound is synthetic hydrotalcite.
As mentioned above, the present invention provides a gas generating agent comprising nitrogenous organic compound as a fuel component and an oxidizing agent for burning it as its major components, to which either or both of metal nitride and metal carbide as the slag forming agent is added, so that the metal nitride and the metal carbide can be allowed to react with the metallic component or oxide thereof contained in the nitrogenous organic compound or the oxidizing agent, to form easily collectable slag. This can provide the results that the fuel component or the metal oxide derived from the oxidizing agent is allowed to react with the nitride or carbide in the process of combustion reaction, to form the high-viscosity slag to thereby produce the slag that can be easily collected by the filtering part and that the nitrogen gas produced by the burning of the metal nitride or the carbonic acid gas produced by the burning of metal carbide can contribute to the inflation of the air bag, together with the nitrogen gas, carbonic acid gas and steam produced by the burning of the nitrogenous organic compound of the fuel compound, and as such can contribute to reduction of the total volume of gas generating agents and reduction of size of the gas generator.
The slag forming metallic component that is allowed to react with the metal nitride or the metal carbide to form the high-viscosity slag in accordance with the type of the metal nitride or the metal carbide may be contained in the fuel component or the oxidizing agent or may alternatively be added in the form of an element (a simple substance) or any independent compound, so that the high-viscosity slag can surely be produced to provide improved slag collecting efficiency.
Particularly preferable gas generating agent compositions include a gas generating agent of system using 5-aminotetrazoles (5-ATZ) as the fuel component and strontium nitrate as the oxidizing agent and adding thereto silicon nitride or silicon carbide; and those based on this system and using hydrotalcites both as the binder and the slag forming metallic component or adding thereto the slag forming metallic component that is allowed to react with the metal nitride or the metal carbide to form the high-viscosity slag.